#include "TRandom.h"
#include "TClonesArray.h"
#include "TTree.h"
#include "TFile.h"
#include "iostream"

class A;


//-----------------------------------------------------------------
class B : public TObject
{
public:
	B():pA(0) {}

protected:
	B& operator=(const B& in)	{return *this;}
	B(const B& in)				{}

public:
	void SetParent(A* in)	{pA=in;}
	A* GetParent()			{return pA;}

	void Clear(const char *opt="") {pA=0;}
	
private:
	A * pA;
	ClassDef(B,1);
};


//-----------------------------------------------------------------
class A : public TObject
{
public:
	A():fB("B") {}

protected:
	A& operator=(const A& in)	{return *this;}
	A(const A& in)				{}

public:
	B* GetB(long idx)	{return reinterpret_cast<B*>(fB[idx]);}
	B* AddB()			{return new (fB[fB.GetEntries()]) B;}
	size_t GetNbrB()	{return fB.GetEntries();}

	void Clear(const char *opt="") {fB.Clear(opt);}
	
private:
	TClonesArray fB;

	ClassDef(A,1);
};


//_________________________________________________________________


//-----------------------------------------------------------------
void create(A *a)
{
	size_t nB = gRandom->Uniform(1,10);

	for (size_t iB=0; iB < nB; ++iB)
	{
		B *b = a->AddB();
		b->SetParent(a);		//comment this line and the error will disappear
	}
}

//-----------------------------------------------------------------
void draw(A *a)
{
	std::cout << "A("<<a<<") contains "<< a->GetNbrB()<<" B's"<<std::endl;
	for (size_t iB=0;iB < a->GetNbrB(); ++iB)
	{
		std::cout << " B("<<iB+1<<") belongs to "<< a->GetB(iB)->GetParent()<<std::endl;
	}
}

//-----------------------------------------------------------------
void WriteRootFile()
{
	TFile *o = new TFile("Test.root","RECREATE");
	TTree *t = new TTree("tree","test");

	A *a = new A();
	
	t->Branch("a","A",&a);

	//size_t nA = gRandom->Uniform(1,10);
	size_t nA=2;

	std::cout <<"Creating "<<nA<<" A's"<<std::endl;
	for (size_t iA=0; iA<nA; ++iA)
	{
		a->Clear();
		create(a);
		draw(a);
		t->Fill();
	}
	o->Write();

	delete o;
}

//-----------------------------------------------------------------
void ReadRootFile() 
{
	TFile *f = new TFile("Test.root");
	TTree *t = reinterpret_cast<TTree*> (f->Get("tree"));

	A *a = 0;
	t->SetBranchAddress("a", &a);
	size_t nA = static_cast<size_t>(t->GetEntries());
	
	std::cout <<"The tree has "<<nA<<" A's"<<std::endl;
	for (size_t i=0; i<nA; i++) 
	{
		cout << "reading "<< i+1<<endl;
		t->GetEntry(i);
		draw(a);
	}

	delete f;
}

//-----------------------------------------------------------------
void testTClonesArray()
{
	gRandom->SetSeed(0);

	WriteRootFile();
	std::cout<< "reading root file"<<std::endl;
	ReadRootFile();
}